One new theory, says physicist Michio Kaku, is that the as yet undetected dark matter of the universe may be ordinary matter that makes up stars, planets and galaxies in a parallel universe. “If a galaxy is hovering above in another dimension,’ says Kaku, “we would not be able to see it. It would be invisible, yet we would feel its gravity. Hence, it might explain dark matter.”
Concealed in the Cosmic Web
A new, far less speculative finding by scientists at the Institut d’Astrophysique Spatiale (CNRS/Université Paris-Saclay), suggests that dark matter remains undetected, concealed in the form of a hot gas in the complex cosmic web. For the first time, the possible signal of the hidden matter has been detected in the filaments of the cosmic web buried 20-year-old spacecraft data through an innovative statistical analysis.
Earlier, 2019 research from the RIKEN Cluster for Pioneering Research and the University of Tokyo, suggests strongly that gas falling along gargantuan filaments under the force of gravity in the early universe triggered the formation of starburst galaxies and supermassive black holes, giving the universe the structure that we see today.
The Weak Signal
The CNRS findings observe “that galaxies are distributed throughout the universe in the form of a complex network of nodes connected by filaments, which are in turn separated by voids. This is known as the cosmic web. The filaments are thought to contain almost all of the ordinary (so-called baryonic) matter of the universe in the form of a diffuse, hot gas. However, the signal emitted by this diffuse gas is so weak that in reality 40 to 50% of the baryons go undetected.”
X-Ray Emission from Hot Baryons
These are the missing baryons, reports Institut d’Astrophysique Spatiale (IAS) hidden in the filamentary structure of the cosmic web, that Nabila Aghanim, Director of Research at the IAS and Hideki Tanimura, a post-doctoral researcher, together with their colleagues, are attempting to detect. In the new study they present a statistical analysis that reveals, for the first time, the X-ray emission from the hot baryons in filaments.
This detection is based on the stacked X-ray signal, in the ROSAT2 survey data, from approximately 15,000 large-scale cosmic filaments identified in the SDSS3 galaxy survey. The team made use of the spatial correlation between the position of the filaments and the associated X-ray emission to provide evidence of the presence of hot gas in the cosmic web and for the first time, measure its temperature.
These findings confirm earlier analyses by the same research team, based on indirect detection of hot gas in the cosmic web through its effect on the cosmic microwave background. This paves the way for more detailed studies, using better quality data, to test the evolution of gas in the filamentary structure of the cosmic web.
Source: H. T Tanimura et al. First detection of stacked X-ray emission from cosmic web filaments, Astronomy & Astrophysics (2020). DOI: 10.1051/0004-6361/202038521
The Daily Galaxy, Max Goldberg, via CNRS
Image credits: top of page, Shutterstock License; text image of cosmic web filaments, : CERN